1. Field of the Invention
The present invention relates to an image forming apparatus employing an electrostatic copying process, such as a copying machine, a facsimile, a printer, and a belt tensioning unit.
2. Description of the Related Art
Examples of image forming apparatuses using electrophotography include an image forming apparatus using a belt-shaped image carrier. In such an image forming apparatus using a belt-shaped image carrier, the belt-shaped image carrier is stretched around and driven to rotate by a plurality of rollers. However, surging of the belt-shaped image carrier may prevent good image formation. Therefore, appropriate tension is applied to the belt-shaped image carrier by using a belt tensioning unit.
Such a belt tensioning unit includes a tension roller serving as a tensioning member and a pressing unit that presses the tension roller against the belt-shaped image carrier. In an operation of image formation, an image is formed with tension applied to the belt-shaped image carrier. However, if the tension is constantly applied, the tension roller and the belt-shaped image carrier have a heavy load. Therefore, the tension is reduced when no image is formed, and when the belt-shaped image carrier is being replaced, for example. In particular, when removing the belt-shaped image carrier, which is one of expendable supplies, from the rollers, the tension applied to the belt is further reduced compared with the case where no image is formed, whereby the belt-shaped image carrier is separated from the rollers to be replaced.
In Japanese Patent Application Laid-open No. 2000-276007, for example, a tension-reducing unit that reduces tension for attaching and detaching a belt is integrated with a belt tensioning unit. Furthermore, in Japanese Patent Application Laid-open No. 2003-216001 in which a belt-shaped image carrier is used as an intermediate transfer body, for example, an intermediate transfer unit including the intermediate transfer body serving as the belt-shaped image carrier and a plurality of rollers supporting the intermediate transfer body is provided, and a cleaning unit that cleans the intermediate transfer body and a belt tensioning unit that applies tension to the intermediate transfer body are configured by one unit.
If the tension-reducing unit for attaching and detaching the belt is provided to the belt tensioning unit that applies tension to the belt-shaped image carrier as disclosed in Japanese Patent Application Laid-open No. 2000-276007, the configuration of the unit is made complicated and the number of components increases. As a result, the space occupied by the unit is made large. By contrast, if the cleaning unit and the belt tensioning unit are configured by one unit as disclosed in Japanese Patent Application Laid-open No. 2003-216001, the configuration of the unit is made large, and it is difficult to attach and detach the cleaning unit and the belt tensioning unit.
Furthermore, such an image forming apparatus using electrophotography is required to be downsized. Therefore, it is desired to downsize functional components and functional units used for the image forming apparatus, and to reduce the number of components and costs.
In view of the background described above, there is a need to provide an apparatus that facilitates replacement of a unit in a space-saving manner without complicating the configuration.